1. Field of the Invention
The present invention relates to a power supply apparatus suitable for a traveling-wave tube.
2. Description of the Related Art
A traveling-wave tube is applied with a variety of voltages such as a heater voltage, a cathode voltage, a helix voltage and a collector voltage. Also, the respective voltages are applied in accordance with a predetermined procedure called an “anode sequence” in order to prevent excessive currents. According to the anode sequence, an anode electrode must be applied with an appropriate voltage at a predetermined delay time after the application of voltages to other electrodes.
Conventionally, a circuit including a relay has been required for powering a traveling-wave tube in accordance with the anode sequence as mentioned above, and power supply apparatuses using a relay have been used in a variety of configurations (for example, see JP-11-149880-A). JP-11-149880-A shows the configuration of a conventional typical power supply apparatus for a traveling-wave tube in FIG. 3.
FIG. 1 is a block diagram illustrating an exemplary configuration of a conventional typical power supply apparatus for a traveling-wave tube. Referring to FIG. 1, the conventional power supply apparatus for a traveling-wave tube comprises high-frequency inverter 91, high-voltage transformer 92, rectifier circuit 93, anode relay 94, relay control circuit 95, and resistor 96.
High-frequency inverter 91 constitutes a primary circuit of the power supply apparatus for a traveling-wave tube. High-voltage transformer 92 transforms the output of high-frequency inverter 91 on the primary side and supplies the resulting voltage to the secondary side. Rectifier circuit 93, which exists on the secondary side, rectifiers the output of high-voltage transformer 92.
One electrode is commonly used as a cathode electrode and a positive heater electrode of traveling-wave tube 97, and is hereinafter called the “heater/cathode electrode.” A negative heater electrode is simply called the “heater electrode.” The output of rectifier circuit 93 is connected to the heater/cathode electrode and to heater electrode of traveling-wave tube 97, and is also connected to an anode electrode of traveling-wave tube 97 and to one terminal of anode relay 94 through resistor 96. Anode relay 94 has the other terminal connected to a helix electrode of traveling-wave tube 97 and to a ground potential, and is controlled by relay control circuit 95 to turn on and off. As relay control circuit 95 turns on anode relay 94, an anode voltage is applied, causing traveling-wave tube 97 to start an amplifying operation.
The conventional power supply apparatuses as mentioned above, however, have the following problems.
The conventional power supply apparatus for a traveling-wave tube illustrated in FIG. 1 requires relay control circuit 95 for controlling anode relay 94.
Since the potential at the anode electrode of traveling-wave tube 97 varies from approximately the ground potential to a potential at the cathode electrode which is applied with a negatively high voltage, a high-breakdown voltage relay capable of withstanding high voltages is used for anode relay 94 which is therefore operated with a high-voltage power supply. Also, a relay driving power supply (not shown) is required for driving anode relay 94. On the other hand, relay control circuit 95, which is involved in sequence control, is generally configured to operate at a low voltage.
Accordingly, isolation must be provided by a vacuum relay or the like between anode relay 94 which operates at a higher voltage and relay control circuit 95 which operates at a lower voltage, thus resulting in a larger size and a higher cost of the power supply apparatus for a traveling-wave tube.